1. Field of the Invention
The present disclosure generally relates to a protective agent used for an image forming apparatus including an image bearing member, a protective layer setting unit for applying a protective agent on the image bearing member, and a process cartridge used for the image forming apparatus.
2. Description of the Background Art
Image forming apparatuses using electrophotography typically produce an image on a transfer medium (e.g., paper) using a procedure like the following: An electrostatic latent image, formed on an image bearing member (e.g., photoconductor), is developed as a visible toner image by attracting charged toner particles thereto, after which the toner image is transferred onto a transfer medium, and fixed thereon by applying heat, pressure, or solvent.
In such an image forming system, the toner particles are used as developer to develop the latent image formed on the image bearing member into a visible image. Such developer may be two-component developer or one-component developer. The two-component developer includes toner particles and carrier particles, in which the toner particles are charged in a process of frictional electrification by agitation with the carrier particles. By contrast, the one-component developer includes toner particles without carrier particles. The one-component developer can be categorized as either magnetic one-component developer or non-magnetic one-component developer, depending on whether or not magnetic force is used to retain toner particles on a developing roller.
Two-component developer is typically used for copiers or multi-functional apparatuses which may need to provide a higher level of performance in terms of high-speed printing and superior image reproducibility because two-component developer has several advantages over single-component developer, such as better charging of toner particles, superior responsiveness for forming toner images during image formation, and long-term stability or durability of the image. By contrast, one-component developer is typically used for small printers, facsimile machines, or the like that may need to provide space and cost savings, because one-component developer can be more simply configured and at lower cost.
Further, there is growing market demand for higher-quality imaging and more durable images, particularly with increased usage of full-color images. In light of such demand for higher-quality imaging, average particle diameter of toner particles continues to be reduced, and particle shape of toner particles has been changed from an irregular shape having sharp edges to a generally spherical shape having fewer sharp edges.
In image forming apparatuses using electrophotography, during imaging the image bearing member such as a photoconductor drum or belt rotating in a given direction is uniformly charged by a charging unit and then exposed to a laser beam to form a latent image thereon. The latent image is subsequently developed into a visible toner image by a development unit and then transferred onto the transfer medium.
After transferring the toner image onto the transfer medium, residual matter, such as toner not transferred to the transfer medium, may remain on the image bearing member. If such residual matter remains on the image bearing member, the image bearing member may not be uniformly charged during a next charging process. Accordingly, after a transfer process, the residual matter may be removed from the image bearing member using a cleaning process to clean the surface of the image bearing member in preparation for a next charging process.
The above-described image forming processes may cause some mechanical damage or electrical stress to image forming apparatus components or devices, such as the image bearing member, the charging device, and the cleaning device, and may result in performance deterioration of such devices. Such deterioration can be lessened by applying lubricant to the image bearing member. The lubricant can be applied as described in following related art.
For example, Published Examined Patent Application No. S51-22380 (hereinafter S51-22380-A) discloses a method of applying lubricant, such as aliphatic acid metal salt, onto a surface of a photoconductor to form a lubricating film on the photoconductor to reduce wear on the photoconductor surface, by which a service life of both the photoconductor and a cleaning blade can be extended.
However, the ability of lubricant having aliphatic acid metal salt such as zinc stearate to provide lubrication soon deteriorates due to a discharge phenomenon occurring on or over the image bearing member during a charging process. Such lubricant degradation may allow toner particles to pass through a gap between the cleaning blade and the image bearing member, resulting in output of a defective image.
In view of such drawbacks of the method disclosed in S51-22380-A, JP-2006-350240-A discloses a method of applying a protective agent having mixed aliphatic acid metal salt and boron nitride to an image bearing member. Such protective agent may maintain its ability to lubricate even when the discharge phenomenon occurs on or over the image bearing member during the charging process because of the lubricating properties of the boron nitride.
However, boron nitride may not be removed easily from the image bearing member due to its higher viscosity, and may be remain stuck to the image bearing member as a film, producing a blurred image.
JP-2005-171107-A discloses a method of applying a protective agent that is a mixture of aliphatic acid metal salt and inorganic fine particles to an image bearing member. Unlike boron nitride, the inorganic fine particles tend not to remain on the image bearing member and thus prevent toner particles from passing through the gap between the cleaning blade and the image bearing member.
Although toner can be prevented from passing through the gap between the cleaning blade and the image bearing member by adding the inorganic fine particles as described above, such passing through of the toner may not be prevented effectively under low-temperature conditions. Further, the aliphatic acid metal salt may fly off the image bearing member and stick to the charge device, by which a charging failure may occur and the charge device may deteriorate faster than the image bearing member.
Further, JP-2007-145993-A discloses a method of applying a protective agent having two higher aliphatic acid metal salt having different numbers of carbon atoms on an image bearing member, wherein such protective agent can be given a suitable shape by an appropriate formation process because the protective agent can be solidified better by using two aliphatic acid metal salts.
However, the lubricating ability of the protective agent may deteriorate due to the combined usage of different aliphatic acid metal salts, by which the passing through of toner and contamination of the charge device may deteriorate. In view of the drawbacks described above, a lubricant that can provide better performance is needed.